Performance recorder for direction indicators



Sept. 5, 1950 T. o. MGCARTHY PERFORMANCE RECORDER ROR DIRECTIONINDICATORS Filed sept 5, 1945 4 Sheets-Sheet l Y., am wmf,

d" m" I A mQ OQ INVENTOR U10/nas 0 MEQ/"fhg A NOR/ vm f Sept` 5, 1950 T.o. MGCARTHY 2,520,948`

PERFRMANCE RECORDER FOR DIRECTION INDICATORS Filed Sept. 5, 1945 4Sheets-Sheet 2 ATTORNEY vFiled sepas, 1945 4 sheets-sheet s Sept-.5,1950 T. o. MGCJAR'THY 2,520,948

yPERFORMANCE RECORDER ECR DIRECTION INDICATORS JNVENTCR.

ATTORNEY Sept. 5, 1950 T. o. MGCARTHY 2,520,945

PERFORMANCE RECORDER FOR DIRECTION INDICATORS Filed Sept. 5, 1945 4Sheets-Sheet 4 wlwm ATTORNEY Patented Sept. 5, 1950 UNITED STATES PATENTOFFICE 2,520,948l PEnFoinvici- Reconoce Fon' DIRc'rIoN INDICATORS'rh-"amas o; McCarthy, Uaei states Navy miracoli saetta 5, 19d; seraiNo. 614,584

'3 oli-dele. (01.346-2) (Granted underA me act ci Marcil '3, 1883, as

amended April 30, 1928i 370 0. G. 757) Thisr invention relates td'photographic recording devices and particularly' to devices forprictographicallyi recordir'ig' data for analyzing pei'- formance errorsof direction"indicators'such as gyrocompas'ses and similar instrumentsunder aetual operating conditions' While underw'ay'at sea or in the air.

Here'toforedirection indicators such as gyro- Compasses and similarinstruments'have generally been tested for errors 'inlaboratoriesashore, as it has not been practical to conduct such tests at sea or'inthe air, (depending on whether the direction indicator is used aboardshipor in an aircraft.) Under such laboratory conditions it has,therefore, not been possible' to determine whether the performanceerrors found ashore are'the same as those obtained under actualoperatingconditions at sea or in the air, and the assumption that' these errorsare' the same in both'cases has been open to "grave doubt. c,

Hitherto it has also notbeen not practicalto determine in a precisemanner, at sea or in the air, Whether such performance errorsA ofdirefction indicators are of the same or different magnitudes' while theship or aircraft is; pursuing dierent courses. For example, it has notbeen practical to determine precisely, while underway, Whetherthe'errors are the' same on an' east-West course' as'on a north-soutlcourse,or how these errors are affected by sudden 'reversals'of course. Thepresent invention seeks tov overcome these obstacles;

One object of the present inve'ntion",r v' accortiingly, is to provide'apriormancerec: derfo'r direction indicators,V` suonl asf gyrocompass orsimilar instruments, wherein the' ,data necessary for determining theerrors thereof arerecorded photographi-calfly' while theship: oraircraft' is underway and maneuvering at sea or `in the air,

Another object is' lQplovde a perform4 corder for yphotograp'liicallyrecording Atl data necessary" for the accur' 'determinano errors ofVdirection stabilize systems' it di'rectionally stable instru. nt, suchvas acompass', controls and causfe's to beA dirctionally" stable adevice of c'onsiderabl'eir'nass rsuclias antenna, searchlightorproj'ec'tor, and receivers ofvelioestypes.

Another object is to provide ameans for measuring theinaccuraci'es of aservo-mechanism controlled by a remotecontrol device Where areferencemark4 or planen common tol both",y cannot easily be `Seen, pr,esablishedi for @amenacen remotely controlledfin its motion by a distantdi- 2 rector device located below the deck of the ship, as in theplotting room.

yAnother Objectis to provide a performance reeerder for directionindicators which is mounted upon oroperativ'ely connected to the outputshaft of a self-synchronous alid'ade or gyrocompas's repeater wherebytherecorder, or its Working parts aremaintained adtoniaticallyin bearingon or near a 4celestial body such as the sun While the various data"Afory determining the errors ofthe direction indicator arel recorldedphotographically atsuitab'le intervals, and at the will of the observer.Another Objectis Vto provide an instrument for photographicallyrecording the data for determining, while underway, the ,errors of adirection indicating or stabilizing system, including the time vandnumber of the observation, the bearing of a heavenly or terrestial bodyvindicated by the direction indicating or stabilizing system, thebearing of the body relative to a reference mark on theship, aircraft orvehicle, and the data necessary to correct the bearing of the body'forthe amount the plane through the line of sight diie'rs from the truevertical plane through the body and to'correct the true' altitude of thecelestial body to' the altitude'with reference to the v-directionindicator from which the observation is being taken.

Another object is to provide an accurate' performance recorder forphotographically recording all data necessary for determining the errorsof a direction indicator or stabilizer as setiorthf in the precedingobjects, and simultaneously vand automatically recording the factorsnecessaryfor correcting the bearing measurements forcrosslevel,`i.e,.for yinaccuracies due to the nonvertical projection of theline ofsight to. a celestial body on the horizontalvv datum ,planeY inA whichthe direction is being measured3-land1 to accomplishY this` by recordingthe amount the plane through the line of sigh-tis tilted fronrthevertical by, reference to the horizon at right angles to the line ofsight.

. all ,data necessary. ,fOr determining `the inaccu- Another object iS.4t provideaniaclt. performance recorder for photographically recordingplane on which the `bearingis measured away y from the horizontal andabout an axis at right angles to the line of sight to a celestial bodyfrom the center of the datum plane, and to accomplish this byphotographically recording the attitude of that plane with reference tothe horizon.

Another object is to provide a performance recorder for photographicallyrecording the data necessary for determining the errors of a directionindicator as set forth in the preceding objects, and also preferablyrecording the tilt of the direction indicator by means of devicesindependent of the horizon, such as spirit levels, whereby observationscan be taken and recorded While entering and leaving port or in otherlocations and under other conditions where a. satisfactory view of thehorizon is not easily obtainable.

Another object is to provide a performance recorder, as set forth in thepreceding objects, that is provided with dials and/ or verniersoperatively connected to the output shaft of the direction indicator,such as the output shaft of a self-synchronous alidade, whereby thereadings of these dials and/or verniers can be recorded photographicallyat suitable intervals, along with the cross-level and preferably alsothe level of thev l instrument, and the time and identifying number ofeach observation.

Another object is to provide a performance recorder for directionindicators wherein a sun telescope is mounted for automatic rotation insynchronism with the output shaft of the direction indicator, thistelescope also having an independent adjustment whereby the cross linesof the telescope can be adjusted back to coincidence with the suns imagewhen an error of the direction indicator causes the cross lines todeviate from such coincidence, means being provided for indicating andphotographically recording the amount that the sun telescope is movedwith reference to the compass repeater, alidade or other directionallystabilized element.

Further objects and advantages of this invention, as well as itsconstruction, arrangement and operation, will be apparent from thefollowing description and claims in connection with the accompanyingdrawings, in which Fig. 1 is a central longitudinal vertical sectionthrough a lpreferred embodiment of the performance recorder of thisinvention;

Fig. 2 is a horizontal section taken along the line 2-2 of Fig. 1;

Fig. 3 is a vertical cross section taken along the line 3--3 of Fig. 1;

Fig. 4 is a vertical cross section taken along the line 4 4 of Fig. 1,showing the instruments` to be photographed, the relative size of a fewof the parts being inconsequentially changed from the relative sizesshown in Fig. 1;

Fig. 5 is a horizontal section taken along the line 5 5 in Fig. 1;

Fig. 6 is a perspective view of the rotary mirror assembly in Fig. 5;

Fig. 7 is a front elevation of the shadow reticle used in the camera;and

Fig. 8 is a fragmentary front elevation of a modification of Fig. 4.

Reference is hereby made to the related copending application Ser. No.649,423, filed February 2l, 1946 by Thomas O. McCarthy and John L.Maulbetsch.

General arrangement In brief, the performance recorder as describedherein includes a housing I9 mounted upon a direction indicator I I(such as a self-synchronous alidade), the output shaft 2o of whichrotates a bearing dial 42 within the housing and an optical cap thereonin one-to-one ratio. Independently mounted on the optical cap is across-level telescope |83, also a conventional sun telescope I2connected to rotate a mirror mount within the optical cap 'I6 and alsoto rotate an azimuth dial adjacent the bearing dial when the telescopeis rotated bodily with the optical cap or independently thereof by atangent screw.

A pair of ports 'Il and I8 ninety degrees apart in the optical cap admitlight rays from the horizon, these being reflected downwardly by fortyvedegree mirrors 88 and 89 in the mirror mount to a xed forty-live degreemirror, which in turn reflects them into the objective of a photographiccamera |23. The camera is also focused upon a. panel containing thedials, an accurate watch 48, an exposure counter G3, and spirit levels68 and 69 arranged to show the tilt of the instrument. A fixed Vernieris arranged adjacent the dials to represent the position of the ship-shead or center line. Optionally provided is an exposure meter |16 and anoptical system for placing the horizon rays in focus with the dials.

Watch, counter and spirit levels. Illumination, such as electricalprojection lamps |20, is provided for illuminating the dials andassociated devices to be photographed.

The observations photographed by the camera are recorded upon a film|21. After the lm is processed, a plot is prepared which indicates, foreach exposure, the error of the direction indicator or stabilizer. Thecompass bearing of the sun, corrected for the cross-level and time ofobservation, is referred to the true bearing of the sun as computed byconventional navigational methods. The difference between the resultsthus obtained is the error of the direction indicator for the particularobservation. By taking repeated observations at suitable time intervalsthe errors of the direction indicator can be charted or shown by graphsfor different conditions of speed, courses steered, roll and pitch ofship or craft and acceleration forces due to changes in course or speed.

Instrument panel and connections Fig. l shows a perfo-rmance recorder,generally designated I0, carrying a conventional sun telescope,generally designated I2, and mounted upon a direction indicator,generally designated II, in this case shown as a conventionalself-synchron- Ous alidade operatively connected to and synchronizedwith the master gyrocompass of the ship, aircraft or Vehicle upon whichthe test is to take place. The self-synchronous alidade is operativelyconnected to and synchronized with the master gyrocompass by aconventional arrangement of self-synchronous motors and generatorsworking through an electronic torque amplifier. The self -synchronousgenerators, one single speed and one 36 speed, are driven by the azimuthmotor of the master compass, which in turn is caused to follow, degreeby degree, the movement of the ship (or plane) in azimuth, about thespace-stabilized, sensitive, gyroscopic element of the compass. Theazimuth motor drives the single and 36 speed synchro generators(self-synchronous generators) and they transmit electrical signals overtwo 3-wire circuits to the synchro receivers in the self-synchronousalidade. In the receiver the incoming signal is used to position therotors of the control transformer (a conventional piece of synchroequipment) and the rotor picks off an j lindireeid-single phase'signaig"which" 'signai fed intoan electronic ampliier'and usedftofcontrolcurrents of*sunicieritaniplitude` to drivei'nduction motors'. Theseinduction v motors drive the `substantial load tothe indicatingmechanism ofi-the self-synchronous alidade and cause it to"fo1iow themaster compass degree' forA "degree" to anl ac- ,curacy'of' '0.'01` offa degree.- The self-synchronous'al'idade l'l isa gyroco'r'npassrepeater having amplificationimp'artin'gpower'sufficient 'to rotate thesun telescope l 25's'oas't0keep it substantialiy inbearingonthesun*or-otherfeiestiai body, or upon fa suitable 'landmarkZ` as thecasemaybe.

The direction indicator 'l1 howeverfca'n consist vof a magnetic com-passrather tnana gyr'co'm'- pass,v with suitable'means 'forjaniplifyin'g thetorque of' the compass card and synchronizing lthe motion ofthesun'telescope 'l'ftherevvifth It can valsoronsistof any remotelyfcontroliedrotatable transmitted from the mastergjvrocornpa'sis;v The repeaterassembly I5 ismo-unted'in'the bovvl- M lovin'eans of gimbai rings E16and l1 to 'aliow for 11o-151 and pitch-oi the ship.

Mounted uponA the' repeater assembly" l5' and secured thereto as lby`th-efcap screws I8 (Fig 1) is a performancerecorder-housing |93 Thelatter contains the vworking parts of the invention and also supportsV'the vsun tei'escopelfZ. The moving parts of the performance' recorderHlVt are' driven from vthe `output shaft 20 of' the direction-indicatorl l this output shaft '2B *being 'rotated- 'in `synchronismwith theCompa'ssrcardof A'theships master gyrocom-pass'by a conventionalelectrical system.'y The output Vshaft ZEVis mounted rotatably in anupper hearing 2l secured'iasjatf! to the repeater lcover 23 4(Fig. f1).A nut '24c'o`mpresses a coverpac-lrin'g ring 25fseatedinan annularrecess 26 in the upper bearing 2|. n

The output shaft "2?) isy provided at its upper end with a taperedportion 2,1 terminating .in a threaded portion 28 'adapteditoreceive a'sh'a'ft'nut V29. Normally, the output shaft 'of the direction indica-tordi, when usedas'a sen-synchronous alidade, 4carries adisc (notshow'n)`provided with anannular lscale divided into degrees. In usingf.

the' present 'inventiomfhoweven this disc is removed and a gear 30-substitutedlfthere'for. Tlhe gear 3i! is provided with 'aitapered'bore-Sl mating with 'the ltapered portion v127|.andsecuredin-posi tion by the shaft nut y29.-

'Ihe gear 35i is provided with peripheral teeth 32 (Fig. l-)f mesh-ingwith-.rapimen V3-8 mounted yon la,v vertical shaft /llisupported at itsl'owerend hy a bearing -bracket'r boltedt'o the'housingit!)4 vrTo Eifs

' coverr plate '3l 'in substantially the saine plane as roy loo g 8 inposition hva-nut threadedfupon the threaded portion 'ii'-ofthestud '4'"Secured tothe-endet?` the rvstudvtii i's a timer 4B; suchv as-anaccurate watch; for determining the -timeiof the observations.V 'Y Thetimer' 48* is maintained in lsulostantial agreement' with "the shipschrono-meter, and itsreadingscorrected accordin'g'to its known errors;The timerf 4-8 preferably readsiinGreenwich cvi-tirne. Since the stud434 does not rotate, the timer 48 isstationary, but is attachedremovablyy tothe-stud rMinany'suitable' manner (not shown) -sothat itcan be 'removedl i:'onvz-:inienftly and another timersubst'ituted. y

Secured as at'El Yand'i tothe housing-99" and the timer -4-8 is a plateor" instrument panel- I5! The plate' 5i)E is 74Vprovidedv with aucircidar-opening -5`3 within whichv an' annular azimuth index dial'flis mounted rotatably hy retaining membersfdi'securedtofthe :pla-te 50.The -dial 54 is provided with VVloevel lgea-r teeth :55 and is drivenfrom a lhevelpiniont'ali.`7 The-azimuth index dial 54 -l`carries arcuateazimuth index Vernier 51 (Fig. 4) having graduations 58 reading upon the.graduation'sd3..v

Mounted adjacent" the graduations 43""is'la fixedships head index'SQC'having vernier vgraduations Gdreadin'g upon the graduations T33 andrepresentingthe position of theships head as "indicated yhy thejackstaii "or center Llinefo'f lthe ship," The ehips head index 59desupported/'hy arms' ti (Fig 4) secured' as at S2 .to the plate tu.

Infthe modification of Fig. 8, th'e'ships head 'index 59a isvmounted.inside the lbea-ring dial to read 'upon the inner graduationsi3d vthereof Vwhereas 'the ygr'aduations `58 4of theazimuth index 51read upon the duplicate `vouter graduations 4'3`b'. This prevents thevazimuthv index graduations 58 from ever being hidden"beneath the shipshead index 5dias is po'ssiiole, though improbable, in the arrangement ofFig. '4.

The position of the ships head index 59" is immaterial so long as the.bearing dial 42' and gear 3U are properly Apositionedl In other words',

when' the ship is underway von a zero course, the zero'graduation oftheh'earing dial 42should coincide 'with' the .zero graduation oftheships head vernierl'.l Furthermore, if vthe ship were steering a zerocourse' in a latitude south of `the equator and the sun happened to bedead ahead at the time, the` vzero of the 'azimuth index 51 wouldcoincide both with the zero of the'ships head index le'andthe zero ofthehearing dial t2,

' assuming'thatthere were no errors in the .direction indicator 11. Itkwould he useful to place the ships head index 59 immediately above the'winding stem g'but' the present .installation it would be concealed"Ihy va mirror' later 'to vloe described.VY

Likewise mounted upon the `plate 5l) is `a counter 63 (Fig. 4)havinganoperating shaft carrying a pinion (i5,I whichis actuated fromthe 4 I photographic" rewind'inechanism .in a manner 05 l`i"counte resetby means of its rewindv knob '67,

Likewise mounted on or adjacent to the plate 50 (Fig. 4) areconventional spirit levels consisting of an athwartship indicator 68 anda fore-and-aft indicator 69. The former is positioned lparallel and thelatter perpendicular to the plate 50. The fore-and-aft indicator 69 isadditionally provided with a forty-live -degree mirror 10 (Figs. 2 and4) whereby it is made visible to an observer looking in the direction ofthe timer 48.

The longitudinal axis 1I12 of the performance recorder I (Fig. 1)preferably is arranged in a fore-and-aft direction, :preferably in thecenter line of the ship. If the instrument is arranged outboard of thecenter line of the ship and a centerline reference mark such as thejackstaif is used, a correction for parallax must be introduced inpositioning the ships head index 59. Thus the bubbles of the athwartshpindicator 68 and fore-and-aft indicator 69 show, with respect to thegraduations upon their tubes, the tilt of the performance recorder I0both athwartships and fore-and-aft.

Telescope and optical system` Mounted rotatably upon the cover plate 31,as by the anti-friction bearings 13 (Fig. 1) operating in annulargrooves 14 and 15, is an optical cap 16. This contains a pair of ports11 and 18 (Fig. arranged ninety degrees apart so as to admit rays fromthe horizon in level and cross-level respectively. The optical cap 16 isprovided with internal gear teeth 16a with which mesh the teeth of anidler pinion 19 driven by a pinion 80 mounted upon the upper end of theshaft 34. In this manner the optical cap 16 is rotated in response tothe rotation of the output shaft 20 of the direction indicator I I.

The optical cap 'I6 is provided with an axial bore 8| within which ismounted rotatably a tubular mirror mount 82 having a flanged portion 83containing an annular groove 84 resting upon anti-friction bearings 85,which in turn run in an annular groove 86 formed in the cover plate 31.The mirror mount 82 is provided with ports 11a and 18a alignedrespectively with the ports 11 and 18. It also contains a rotary mirrorassem- 'bly 81 (Figs. l and 6) consisting of a pair of mirrors 88 and 89disposed substantially in the axis of rotation of the mirror mount 82and arranged substantially at forty-live degree angles to the horizonrays entering the ports 11 and 18 so as to reflect these rays downwardlyparallel to the axis of rotation of the mirror mount 82. Consequentlythe mirrors are approximately of triangular shape and intersect alongthe diagonal line 90.

The periphery of the flanged portion 83 of the mirror mount 82 isprovided with gear teeth 9| meshing with a pinion 92 upon the upper endof a shaft 93. The latter is rotatably supported at 94 in the coverplate 31 and on its lower end carries the bevel pinion 56. Disposedbelow the rotary mirrors 88 and 89 is a xed mirror 95 mounted upon abracket 96 secured as at 91 to the cover plate 31 (Fig. l). The mirror95 is arranged with its plane substantially at forty-five degrees to therays reflected downwardly from the rotary mirrors 88 and 89.

The end portion 98 of the mirror mount 82 has a collar |00 pinned as at99 to a shaft |0| which extends upwardly through a bore |02 in acupshaped telescope support |03 (Fig. l) that mates with and is mountedrotatably upon a cylindrical .boss |04 projecting upwardly from theoptical lcap 16.

8 I The telescope support |03 is provided with handle |05 whereby it canbe rotated by the operator. The telescope support |03 is also providedwith an annular seat |06 for rotatably receiving the cylindrical portion|01 of the telescope mount |08.

The cylindrical portion |01 is provided with an arcuate worm gearportion |09 which is engaged by a worm I|0 mounted upon a tangent screwshaft ||I and rotatable by means of a knob ||2. The tangent screw shaftIII is mounted in suitable bearings (notshown) and provides a neadjustment for rotating the telescope mount |08 relatively to thetelescope support |03. The telescope mount |08 is provided with anoutwardly projecting portion 3 which normally carries a Vernier II4. Theshaft |0I enters a bore |I5 in the telescope mount |08 and is pinnedthereto so that when the sun telescope I2 is swung to and fro, thismotion is transmitted through the shaft I0 I to the mirror mount 82.

Rising from the telescope mount |08 are spaced arms I I6 carryingtrunnions ||1 upon which the sun telescope I2 is supported. A pointer|I8 secured to the telescope I2 at its axis of support cooperates withan arcuate degree scale |I9 in such a manner as to indicate the amountof tilt of the sun telescope I2. The latter is provided with a reticle(not shown) preferably having central cross lines and vertical stadialines spaced at equal distances from the central vertical cross line andon opposite sides thereof. The spaced vertical stadia lines areseparated by the angular distance subtended by the suns disc. Anobserver can measure the altitude of the sun above the horizon with asextant and swing the sun telescope I2 about its trunnions I I1 untilthe pointer I I8 indicates the same altitude upon the scale II9. Anotherobserver looking through the telescope I2 will then find that the stadialines thereof are substantially aligned upon the opposite edges of thesuns disc, provided of course that the sun telescope I2 is rotated tothe correct azimuth. The sun telescope I2 is provided with the usual rayfilters or crossed polarizing plates (not shown) to cut down theintensity of the suns image and avoid injury to the eyes of theobserver.

Photographic system To illuminate the plate 50 and its associated dialsand instruments (Fig. 2), the housing I9 is provided with suitableincandescent bulbs |20 having laments I2| energized from any suitablesource of electricity. The bulbs |20 can be of a type used in smallmotion picture projectors. Curved reflectors |22 are provided toconcentrate the light from the laments I2I and direct it toward theplate 50. The reflectors |22, at the same time, prevent extraneous lightfrom reaching the photographic apparatus.

Arranged in the forward end of the housing I9 is a photographic camera,generally designated |23, for photographing the plate 50 with itsassociated dials and instruments and also the images of the horizon incross-level and level as reflected by the mirrors 88, 89 and 95. Thecarnera |23 can be of any suitable type, the type known by the tradename Leica being convenient for this purpose. The details 0f the camera|23 are conventional and form no part of the present invention. Thecamera |23 is provided with an objective I 24 which is focused by afocusing knob |25 so that it will produce a sharp image of the plate 50and its associated dials and instru- Operation Preliminary to theoperation of the performance recorder I0, it is assumed that the properadjustments have been made so that the bearing dial 42 and azimuth index51 read properly relatively to the zero of the ships head index 50. Thetimer 48 is also carefully checked by the ships chronometer andinstalled in its proper position (Fig. 1). The camera |23 is loaded witha suitable supply of iilm and is inserted in its mount |32 and securedrigidly. The sun telescope I2 is also adjusted properly and thedirection indicator I I precessed so as to bring the cross wires of thetelescope I 2 into alignment with the jackstai of the ship, assumingthat the direction indicator I I is mounted on the center line of theship. If it is mounted to one side of this center line and the jackstaffis still used for alignment, the position of the ships head index 59must be corrected for parallax.

The ships head index 59 is now adjusted to read the true bearing of theships head by the bearing dial 42. The sun telescope I2 is then trainedat a denite angle on either bow and the azimuth index 54 adjusted sothat the bearing of the telescope I2 reads the same angle as the angleto which the telescope I2 is trained, and in the same direction.Meanwhile the tangent screw worm is adjusted by the knob ||2 so that itlies approximately midway in the arcuate worm gear teeth |09, so as topermit an adjustment of about four or five degrees in either direction.

It is furthermore assumed that the level and cross-level optical systemshave been lined up with reference to a surface plate and a transit priorto the removal of the instrument from the shop.

The electrical cables for supplying current to the illumination bulbs|20 are connected to a source of electricity and the observations areready to be proceeded with. Ordinarily the iris diaphragm |14 of thecamera |23 will be set in its wide open position and the adjustment ofexposure made by regulating the shutter speed. The ray filters,diaphragms or stops, or other-suitable means for regulating theintensity of the light coming from the horizon through the ports 11 and18 are adjusted so that the proper light intensity is obtained, and thephotoelectric cell unit |11 of the exposure meter |16 is swung into thepath of these rays and the proper exposure determined. As theillumination of the plate 50 and its associated dials and instrumentswill be of a substantially constant value, the shutter speed will beregulated for this value. Extensive experience with the invention hasdemonstrated that the intensity of the daylight can be controlledsuitably to match the artificial illuminationrof the plate 50, withinthe latituderof the film, and Very satisfactory film negatives obtainedunder practically all operating conditions.

The direction indicator II (such as a self-synchronous alidade) is nowcut in on the gyrocompass system, the illumination turned on, thecounters 63 and |60 set at zero and the sun telescope I2 adjusted sothat its spaced vertical stadia lines span the suns disc. Theperformance recorder I 0 is steadied in cross-level by the crosslevelobserver sighting through the cross-level telescope |83 and holding thecross line of the reticle thereof vupon the horizon at right angles tothe line of sight to the sun.

Assuming that the film |21 has been transported into position to makethe first exposure, the first observation is then recorded by depressingthe exposure button III. The latter can be provided with a flexiblecable release of a conventional type (not shown). After the exposure isthus obtained, the film is transported and the shutter rewound byturning the lm rewind knob |50. This action also moves the counters B3and |60 ahead one unit. The next observation is photographed in asimilar manner. These operations are repeated at suitable intervals,such as a few seconds apart, over a period of several hours, as the filmmagazine ordinarily holds several hundred exposures.

Meanwhile the direction indicator I I will maintain the spaced verticalstadia lines of the sun telescope I2 very closely in alignment with theopposite edges of the suns disc. Errors in the direction indicator I orthe gyfocompass system will cause these stadia lines to deviate fromsuch alignment with the suns disc, and this deviation is a measure ofthe error to be determined. When, due to this error, the stadia linesdrift away from alignment with the opposite edges of the suns disc, theoperator brings them back into alignment by turning the knob I2operating the tangent screw worm I|0. When the image of the suns disc isfairly braced between the vertical stadia lines, the center of the sunsdisc coincides with the central vertical cross line. When the operatorturns the tangent screw knob I|2 he automatically shifts the azimuthindex 51 and the rotary mirror unit 81 used for establish ing thecross-level and level corrections.

Ordinarily, observations are taken with the ship steering variouscourses and during the turns made as a result of changing courses. Undersuch conditions it is found that the gyroccmpass oscillates and produceserrors, particularly when the helm is put hardover and a sharp turnexecuted. The observations thus photographed enable these errors to beaccurately determined.

When the observations are completed and the nlm has been processed, apot is prepared which, for each exposure, will indicate the error of thegyrocompass and self-synchronous alidade systems, assuming that thelatter is used as the direction indicator I I. The compass bearing ofthe sun, corrected for the cross-level and time of observation, isreferred to the true bearing of the sun as computed and readilyavailable according to methods set forth in various Naval HydrographicOice publications. The difference between the two bearings is the errorof the direction indicator which it is desired to obtain. These errorsare plotted against the time and for each course, and a running recordof the variation of these errors is thereby obtained. From these graphsthe performance of the particular direction indicator II can bedetermined accurately under varying conditions and a permanent recordobtained under water-borne or air-borne operating conditions.

The construction and operation of the instrument has been particularlydescribed in connection with its installation aboard a ship. It will beunderstood, however, that the same instrument can be employed todetermine the errors of direction indicators mounted upon aircraft orupon land vehicles, following an analogous procedure.

It will -be further understood that a terrestrial landmark, ifavailable, can be, and frequently is, used instead of a celestial body.The operational procedure is the same in taking observation but adifferent method of computation must be used to determine the truedirection of the landmark from the observer at the instant theobservation is made.

Dejm'tions In the specification and claims hereof it will be understoodthat the use of the term sun comprehends other celestial bodies such asstars or planets, the sun being the most conveniently used body and theone most frequently selected.

The term compass as used herein is defined as a device having means formaintaining itself in a substantially constant angular relationship withthe 4projection of the earths axis on the horizontal plane at thelocation of the device.

The term level as used herein is dened as the angular tilt Iof anassumed datum plane of the instrument, suchas the compass card, about ahorizontal axis perpendicular to the line of sight of the sun telescope.

The term "cross-level as used herein is dened as the angular tilt of anassumed datum plane of the instrument, such -as the compass card, abouta horizontal axis in the line of sight of the sun telescope.

Various modiiications and changes can be made in the subject deviceWithout departing from the scope of the invention.

The invention described herein may be manufacured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

I claim:

1. An instrument for recording the performance characteristics of adirection indicator having a movable direction-indicating element, saidinstrument comprising a ships bearing indicator adapted to ibe rotatedby said element, a stationary index representing a xed point ofreference on the ship adjacent thereto, a rotatable support -adapted tobe driven by said element, a suns azimuth nder mounted on said support,a suns azimuth indicator carried by said inder. optical meansvr mountedon said azimuth rrder for transmitting horizon rays in cross-level andlevel, a time indicator, and means for simultaneously recording thereadings of said indicators and the transmitted image formed by saidhorizon rays.

2. An instrument for recording the performance characteristics of adirection indicator having a movable direction-indicating element andhaving an output shaft, said instrument cornprising a housing mountedupon such direction indicator, a bearing dial `within said housingrotated by such shaft in one-to-one ratio, an optical cap on said dial,a cross-level telescope mounted independently on said cap, a suntelescope linked to a mirror mount Within said cap to rotate said mirrormount, and linked to an azimuth dial adjacent said bearing dial torotate said azimuth dial with said optical cap, means to rotate saidazimuth dial independently of said telescope, a pair of ports in sai-dcap spaced degrees apart, said ports being adapted to admit light raysfrom the horizon so that such rays are reflected by said mirror mountinto a eld of view Within said housing, a panel in said housing in saideld of view, said panel carrying said dials, a watch, an exposurecounter and a plurality of spirit levels arranged to show the tilt ofthe instrument, a xed Vernier adjacent sai-d dials and in said ield ofview, said Vernier representing the position of the ships head, means toilluminate said field of view, and means to photograph said dials anddevices in said eld of View.

3. The combination recited in claim 2 and an optical system carried insaid housing, said optical system being adapted to place said horizonrays in focus with the dials and devices that appear in said field ofView.

THOMAS O. McCARTI-IY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 790,871 Camden May 23, 19051,073,832 Wlodzimirski Sept. 23, 1913 1,223,686 Frisch Apr. 24, 19171,432,570 Roux Oct. 17, 1922

